If you are expecting a big change in what he likes (and you would be right, there is a huge change in maturity and understanding and when they start school they become interested in what school friends have) why not wait until then? Put the money away now but wait and see what he is into and what is in the shops nearer the time.

My daughter started reception last year and there was a noticeable change. However, lego and playmobil still VERY popular with boys and girls. Peppa pig phase replaced by Disney princesses , moshi monsters and Hello Kitty. Doc mcstuffins still popular. Still into dolls (shes only 4) but Barbies are becoming an interest. Crazes amongst boys are Angry Birds, Star wars, pirates and transformers.